1. Field of the Invention
The present invention relates to a real-image finder.
2. Description of the Related Art
As is well known, a conventional real-image finder includes an objective optical system which forms an object image on a primary image forming surface in a field frame, an ocular optical system through which the object image formed on the primary image forming surface can be viewed, and an image erecting optical system which inverts the image formed by the objective optical system in the vertical and horizontal directions. In the real-image finder, if foreign matter (such as dust) sticks to the primary image forming surface, the dust can be viewed together with the object image through the ocular optical system. One solution to this problem is to isolate (seal) the finder entirely whereby no foreign matter can enter the finder. However, it is difficult to perfectly isolate the finder due the complicated structure thereof.
The assignee of the present application has proposed another solution in U.S. Pat. No. 5,822,626, in which a seal block unit (dust-proof block) is provided, which only seals the vicinity of the image forming surface on which the object image is formed by the objective optical system. The dust-proof block is made of a hollow rectangular body which opens at the front and rear ends thereof in the optical axis direction and which is provided on the front and rear end surfaces thereof with peripheral grooves in which sealing members, each being in the form of a string (cord), are press fitted. The sealing members are held between the end surfaces of the hollow block and transparent members (e.g., lenses) to provide a dust-proof structure. A liquid crystal display (LCD) is provided in the vicinity of the image forming surface within the hollow block. If the actual picture surface is not identical to the field of view of the finder (for example, upon photographing at close-up mode or panoramic mode), the voltage to be applied is controlled whereby a portion of the liquid crystal display (LCD) becomes clouded to vary the size of the field frame. The hollow block is provided with an insertion hole through which conductors connected to the LCD extend. The insertion hole is also sealed by a sealing member.
In the case where a switching device for switching the size of the field frame is formed by the LCD mentioned above, the seal block can be rectangular. However, in a mechanical switch in which the size of the field frame is altered mechanically, if the seal block which seals the vicinity of the image forming surface is rectangular, it is difficult to arrange the field frame size switching mechanism within the rectangular block. In general, it is difficult to arrange any member including the field frame size switching member in a rectangular block.
It is an object of the present invention to provide a real-image finder having a dust-proof structure in which the vicinity of the image forming surface is sealed, and components can be easily assembled or incorporated in the vicinity of the sealed image forming surface.
To achieve the object mentioned above, according to the present invention, there is provided a real-image finder including an objective optical system which forms an image of an object onto a primary image forming surface; an ocular optical system through which the object image formed on the primary image forming surface can be viewed; and an image erecting optical system which inverts the object image formed by the objective optical system, in the vertical and horizontal directions. The real-image finder includes: a rectangular body which includes a main frame having a generally U-shape section which is uniform in the optical axis direction, the main frame being provided with a pair of front and rear end openings in the optical axis direction and a side opening, and a separate cover which is adapted to close the side opening of the main frame; a field frame that is supported within the rectangular body on the primary image forming surface; a pair of transparent members which close the pair of front and rear end openings of the rectangular body; at least one sealing member for sealing a contact portion between the main frame and the cover, and for sealing a gap between the rectangular body and the transparent members.
Preferably, the main frame includes, on the outer surface of two opposing sides thereof, a plurality of engagement projections; and the cover comprising a plurality of plate-like extensions having holes in which the engagement projections are engaged, wherein the main frame and the cover are engaged by the engagement of the engagement projections and the holes of the extensions.
Preferably, the main frame of generally U-shape section is provided with a pair of opposed parallel wall portions, the cover covering the side opening; wherein the main frame includes: a pair of linear grooves which extend in a direction parallel with the optical axis and which are provided on the open side of the opposed parallel wall portions of the main frame; at least one sealing member being fitted into the linear grooves.
Preferably, the rectangular body constituting the main frame and the cover further includes: a pair of peripheral grooves in which the transparent members are loosely fitted and which are formed on the inner surface of the main frame, the peripheral grooves being located at different positions in the optical axis direction and on opposite sides of the primary image forming surface; at least one sealing member being inserted into the peripheral grooves to stably hold the transparent members in the peripheral grooves and to seal the gap between the transparent members and the peripheral grooves.
Preferably, the linear grooves are connected at the opposed ends thereof to the respective peripheral grooves.
Preferably, the sealing members include a first sealing member which is continuously arranged in one of the peripheral grooves and one of the linear grooves, and a second sealing member which is continuously arranged in the other peripheral groove and the other linear groove.
Preferably, the sealing members are made of a resilient material.
Preferably, the sealing members are made of an air permeable material.
Preferably, the sealing members are in the form of a cord.
Preferably, a field frame switching mechanism is further provided which mechanically switches the size of the field frame in the rectangular body.
Preferably, the field frame switching mechanism includes: a pair of U-shaped grooves which are provided on the side-opening side of the parallel wall portions of the main frame, the pair of U-shaped grooves lying in a line perpendicular to the optical axis; and a movable field frame member separate from the field frame, supported in the U-shaped grooves so as to rotate about rotation shafts between a lowered position (in which the movable field frame member is located on the optical axis in the close vicinity of the primary image forming surface) and a raised position (in which the movable field frame member is retracted from the optical axis).
Preferably, the U-shaped grooves intersect the linear grooves; the rotation shafts of the movable field frame member projecting above the bottom surfaces of the linear grooves to reduce the distance from the cover; and the sealing members inserted in the linear grooves being located on top of the rotation shafts.
Preferably, one of the U-shaped grooves extends to the outside of the rectangular body, wherein the movable field frame member can be rotated from the outside of the rectangular body via the above-mentioned U-shaped groove.
Preferably, one of the rotation shafts extends along the one of the U-shaped grooves wherein one of the rotation shafts includes a rotation operation member having an operation pin.
Preferably, an association member is also provided, the association member including a pair of pin holding arms which hold therebetween the operation pin in order to lower and raise the movable field frame member.
Preferably, at least one of the pair of transparent members is a lens.
According to another aspect of the present invention there is provided a real-image finder having an objective optical system which forms an image of an object onto a primary image forming surface; an ocular optical system through which the object image formed on the primary image forming surface can be viewed; and an image erecting optical system which inverts the object image formed by the objective optical system, in the vertical and horizontal directions; the real-image finder including: a rectangular body which includes a main frame having a generally U-shape section which is uniform in the optical axis direction, the main frame being provided with a pair of front and rear end openings in the optical axis direction and a side opening, and a separate cover which is adapted to close the side opening of the main frame; a field frame that is supported within the rectangular body on the primary image forming surface; a pair of transparent members which close the pair of front and rear end openings of the rectangular body; a first sealing member which is continuously arranged for sealing a part of a contact portion between the main frame and the cover, and also for sealing a gap between the rectangular body and one of the pair of transparent members; a second sealing member which is continuously arranged for sealing the other part of the contact portion, and also for sealing a gap between the rectangular body and the other of the pair of transparent members.
Preferably, the main frame includes, on the outer surface of two opposing sides thereof, a plurality of engagement projections; and the cover including a plurality of plate-like extensions having holes in which the engagement projections are engaged, wherein the main frame and the cover are engaged by the engagement of the engagement projections and the holes of the extensions.
Preferably, a pair of linear grooves which extend in a direction parallel with the optical axis and which are provided on the side-opening side of the opposed parallel wall portions of the main frame are also provided; the first and second sealing members being fitted into each of the linear grooves; and a pair of peripheral grooves in which the transparent members are loosely fitted and which are formed on the inner surface of the main frame, the peripheral grooves being located at different positions in the optical axis direction and on opposite sides of the primary image forming surface; the first and second sealing members being inserted into the peripheral grooves to stably hold the transparent members in the peripheral grooves and to seal the gaps between the transparent members and the peripheral grooves; wherein the linear grooves are connected at the opposed ends thereof to the respective peripheral grooves.
Preferably, the sealing members are made of a resilient material.
Preferably, the sealing members are made of an air permeable material.
Preferably, the sealing members are in the form of a cord.
According to another aspect of the present invention, there is provided a seal unit for a real-image finder having an objective optical system and an ocular optical system, the seal unit including: a rectangular body which is composed of a main frame of a generally U-shape section which is uniform in the optical axis direction, the main frame being provided with a pair of end openings in the optical axis direction and an open side, and a separate cover which is adapted to close the open side of the main frame; a field frame that is supported in the rectangular body so that the field frame is positioned on a primary image forming surface of the objective optical system; a pair of transparent members which close the pair of end openings of the rectangular body; at least one sealing member for sealing a contact portion between the main frame and the cover, and for sealing a gap between the rectangular body and the transparent members.
Preferably, the main frame includes a groove formed inside wall thereof to receive said pair of transparent members before the separate cover is attached to the main frame, the groove being positioned on a plane perpendicular to the optical axis.
Preferably, a sealing member is inserted between the bottom of the groove and the peripheral surface of the pair of transparent members.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 10-1509 (filed on Jan. 7, 1998) which is expressly incorporated herein by reference in its entirety.